1. Field of the Invention
The present application generally relates to suspension systems. More specifically, the present application relates to a suspension system for snowmobiles.
2. Description of the Related Art
Snowmobiles generally have a pair of right and left slide rails for guiding a drive track under a vehicle body frame. Suspension systems usually include shock absorbers and linkage mechanisms, including extendable members, interposed between the vehicle body frame and the slide rails so that the vertical distance between the body frame and the slide rails can increase and decrease. Some snowmobiles have rear suspension structures with four-node linkages that have generally parallelogram configurations.
Some snowmobile suspension systems have a relatively small four-node linkage positioned relatively close to the vehicle body frame, as shown in FIGS. 9A and 9B, which will be described later in connection with those Figures. When the distance between the vehicle body frame and the slide rails is reduced to the minimum, the four-node linkage is changed in shape from a parallelogram inclined rearward to a parallelogram slightly inclined forward. Since almost the whole four-node linkage is located inside the vehicle body frame and the parallelogram thereof is small in configuration, large forces are exerted on the nodes and the linkage members when the four-node linkage is contracted. Thus, the nodes and the linkage members must be suitably sized to provide the necessary strength. Also, the extendable length of the extendable member cannot be too large. Accordingly, the slide rails can only be adjusted through a small angle with respect to the vehicle body frame and the surface on which the snowmobile is running. Thus, it is difficult to keep these snowmobiles in a properly adjusted, stable condition while traveling.
In other snowmobile suspension systems, a four-node linkage has a relatively larger, generally parallelogram configuration, as shown in FIGS. 10A and 10B, which will be described later in connection with those Figures. When the distance between the vehicle body frame and the slide rails is reduced to the minimum, the four-node linkage is changed in shape until the parallelogram becomes almost flat (i.e., all of the linkages generally lie parallel to each other). In these snowmobile suspension systems, although the parallelogram of the four-node linkage is large, the sides of the parallelogram overlap in its most contracted state. Thus, in some instances, the four-node linkage does not compensate for pitching to an adequate extent to provide a comfortable ride.